Enhanced and suppressed effects of ionic liquid on the photocatalytic activity of TiO 2
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Enhanced and suppressed effects of ionic liquid on the photocatalytic activity of TiO2 Lifang Qi • Jiaguo Yu • Mietek Jaroniec
Received: 8 October 2012 / Accepted: 17 January 2013 / Published online: 30 January 2013 Springer Science+Business Media New York 2013
Abstract The effects of a room temperature ionic liquid, 1-butyl-3-methylimidazolium terafluoroborate ([Bmim]BF4), on the photocatalytic performance of Degussa P25 TiO2 were investigated. Also, the photocatalysis mechanism was systematically analyzed by conducting different reactive radical trapping experiments. The results showed that photogenerated electrons were the main reactive species involved in the photocatalytic degradation of methyl orange (MO), while •OH radicals and photogenerated holes played an important role in the photocatalytic decomposition of rhodamine B (RhB). The addition of ionic liquid (IL) could slightly enhance the photocatalytic degradation rate of MO because adsorption of [Bmim]? ions on the TiO2 surface not only enhanced traping and transfer of photogenerated electrons, but also facilitated adsorption of negatively charged MO. On the contrary, IL suppressed the degradation rate of RhB because [Bmim]? on the TiO2 surface not only hindered the access of positively charged RhB to TiO2, but also restricted the diffusion of positively charged holes to the TiO2/solution interface. Keywords Titania (TiO2) Photocatalytic activity Ionic liquid Adsorption
L. Qi J. Yu State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122#, Wuhan 430070, People’s Republic of China e-mail: [email protected] M. Jaroniec (&) Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44242, USA e-mail: [email protected]
1 Introduction Heterogeneous semiconductor photocatalysis is considered as one of the most promising technologies for the elimination of organic contaminants in environment and for the production of H2 by water splitting (Fujishima and Honda 1972; Hoffmann et al. 1995; Park et al. 2006; Xiang et al. 2012a, b; Li et al. 2011; Zhang et al. 2011a, b). In particular, TiO2-based photocatalytic purification of air and water has attracted a widespread attention (Choi et al. 1994; Cheng et al. 2007; Tan et al. 2012; Fan et al. 2011; Liu et al. 2010; Xiang et al. 2011a, b; Liu et al. 2011; Zhang et al. 2008; Li et al. 2003; Wang et al. 2009). However, the photocatalytic performance of TiO2 must be further enhanced from the viewpoint of practical applications and commercial benefits (Ksibi et al. 2008; Frank and Bard 1977; Yu et al. 2010; Qi et al. 2011). Since heterogeneous photocatalytic reactions mostly take place at the liquid/solid and/or gas/solid interfaces, the properties of TiO2 such as the phase structure, chemical composition, surface defects, surface area, and the concentration and type of surface functional groups are critical for the photocatalytic reaction efficiencies. Up to now, TiO2 surfaces have been widely modified via manipulating th
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